----- Original Message -----
Sent: Sunday, March 19, 2006 12:09
PM
Subject: LF: Re: LOOPS V VERTICALS
Jim you are confusing the
discussion by introducing a noisy local enverionment, where no doubt its a
loop or nothing to null out the noise.
My argument made it clear that I
was considering the merits of loops v verticals especially the smaller ones in
a good quiet environment, the only way to compare both as regards efficiency
and signal capture.
de Mal/G3KEV
The argument about loops and
verticals in noisy locations has been discussed many times
before.
Dear LF Group,
At M0BMU, the original motivation for using
seperate RX antennas was the increasing 50Hz-related noise level on the
TX vertical. This seems to be due to pick-up from the house mains wiring, but
moving the vertical further from the house would result in reduced possible
length, and it is short enough already!
Remote vertical antennas worked fine as far
as eliminating mains noise was concerned, but did nothing to reduce
distant sources of QRM such as Loran. Here I have to use quite selective
antennas (the broadband active-whip type of antenna is not really workable
here due to the 20V/m MF signal levels from Brookmans Park). For some time I
used single loops oriented to null out the Lessay Loran signal, and I
estimated this reduced the noise floor for most European signals by 6dB or so,
which made quite a few more stations audible. I found that much
experimentation was needed to find suitable positions for the loops where they
would null out Loran, but not pick up 50Hz noise at the same time - loops seem
to be more sensitive to this type of QRM.
Then the Rugby Loran started up, and the band
noise level in aural reception bandwidths (e.g. 300Hz) increased by 15dB,
wiping out many of the weaker signals at this QTH. I countered this
using both loop and vertical antennas phased together to provide two
adjustable nulls aimed at Rugby and Lessay. This brought the situation for
aural reception of European sigs to about the same place as it was before -
but most signals coming from the west are attenuated by the overall
directional properties of the system.
So, for aural
signal reception at this location in SE England, currently neither loops
nor vertical antennas by themselves work very well, allthough quite good
results are achieved by using a phasing system with both types of antenna to
null out the Loran.
For narrow-band QRSS, etc. signals, the situation
is different, since provided the received signal frequency does not coincide
with a Loran line, Loran does not matter too much. There does not seem to be
much to choose between the loop and the vertical most of the time, however
under quiet band conditions with little QRN I have found that if I use the
phased loop and vertical antennas, and reverse the relative phase of the
antennas to favour signals from the west (i.e. for transatlantic reception),
the band noise is reduced by several dB on the spectrogram compared to either
antenna by itself - I suspect this may be due to a reduction in
"Luxembourg effect" noise originating from Europe to the east.
So here I find it neccessary to use both
types of antenna simultaneously, if I want to achieve good results. This is
mostly to overcome the effects of man-made QRM and to enable aural reception
of signals, which are perhaps the main differences between my situation and
the others who have commented.
Cheers, Jim Moritz
73 de M0BMU
